Patients suffering from renal failure who undergo hemodialysis treatment require their blood to be readily accessible for such treatment. To avoid repeated puncturing of blood vessels, a technique has been developed in the prior art, wherein a graft is implanted that acts as a shunt between an artery and a vein, such graft being aptly referred to as an arterio-venous (AV) shunt graft. Typically, the AV graft is of relatively long length to provide maximum length for needle puncturing. Because of the relatively long length, the AV graft typically has a longer length than the spacing between the relevant artery and vein, and, as such, is often bent into a U-shape. For implantation, two relatively shallow channels are subcutaneously “tunneled” into the necessary U-shaped pattern, with a tunneller or guidewire being used to draw the AV graft into proper position. The ends of the graft are sutured, or are otherwise connected to, the selected artery and vein.
To limit the amount of blood diverted through the AV graft, and away from artery, the AV graft may have a tapered end at its arterial connection. In this manner, blood flow through the AV graft is restricted, without sacrificing surface area for needle puncture sites.
Although conventional AV grafts may provide relief for the vasculature, sealing of puncture sites therein is of major concern because of blood loss, as well as concern for the overall structural integrity of the graft. One approach to this problem has been in delaying a minimum number of days, often as long as two weeks or more, after implantation before puncturing the AV graft. The minimum delay period allows fibrotic tissue to surround the graft. Thus, upon puncturing, the body is naturally able to cause a clot and restrict blood loss.
A second and different approach has been the use of self-sealing grafts, which typically rely on fibrous material or sealant material to seal over a puncture. Examples of this approach are found in U.S. Pat. No. 4,619,641 to Schanzer; U.S. Pat. No. 5,192,310 to Herweck et al.; and U.S. Pat. No. 5,700,287 to Myers et al. Because of the additional self-sealing material applied to this set of grafts, these AV grafts often have relatively large diameters.
Due to the repeated puncturing of AV grafts, AV grafts have a limited life, regardless of design. Whereupon the structural integrity and/or the sealing ability of the AV graft becomes excessively compromised, a new AV graft is implanted into the patient at a new location. Patients who require hemodialysis over extensive periods of time may have multiple AV grafts implanted in them. As is readily apparent, it is desired to provide an AV graft having an extended life, to minimize the need for additional AV graft implantations in a patient.